Mars Global Surveyor
AKA: MGS. Status: Operational 1996. First Launch: 1996-11-07. Last Launch: 1996-11-07. Number: 1 . Height: 1.80 m (5.90 ft).
Mapping operations begin in March 1998. After collecting data for its prime mission of a full Martian year (nearly two Earth years), the spacecraft continued in operation for nearly ten years, observing changes to the Martian surface and acting as a data relay station for follow-on Mars missions.
Mars Global Surveyor was the first mission of the Mars Surveyor Program, which was an aggressive series of orbiters and landers designed to provide new global and close-up images of Mars. After the initial elliptical capture orbit, months of thruster firings and aerobraking maneuvers were used to reach the nearly circular mapping orbit.
The spacecraft used X-band uplink at 500 bps and X-band and Ka-band downlinks at 85.3 kbps maximum. The 1.5 m diameter, articulated high gain antenna was mounted on a 1.5 m boom. Four low-gain antennas provided backup communications. The dual-mode propulsion system (MMH/NTO or MMH monopropellant) had one 596 N and twelve 4.45 N thrusters. Total propellant load was 361 kg. The passive thermal control design was 3-axis stabilized with 10 mrad control and 3 mrad knowledge using reaction wheels, thrusters, sun sensors, horizon sensors, celestial sensors, and an IMU. Four articulated 1.7 m x 1.8 m solar panels (2 GaAs, 2 Si) provided 656 watts (980 W max) and fed two 20 Ahr NiH2 batteries. The MIL-STD-1750A-based central computer had a total data storage capacity of 3 gigabits.
Total science payload mass was 78 kg.
NASA NSSDC Master Catalog Description
The Mars Global Surveyor (MGS) orbited Mars over a seven year period and collected data on the surface morphology, topography, composition, gravity, atmospheric dynamics, and magnetic field. This data will be used to investigate the surface processes, geology, distribution of material, internal properties, evolution of the magnetic field, and the weather and climate of Mars.
The spacecraft itself is a rectangular box approximately 1.17 x 1.17 x 1.7 meters in size, made up of two parts, the equipment module and the propulsion module. All instruments except the magnetometer are stored on the nadir equipment deck, on one of the 1.17 x 1.17 meter surfaces. This is the top of the equipment module, which is 0.735 m high. The main thruster and propulsion tanks are on the opposite side from the instruments, on the propulsion module, which is approximately 1 meter high. Two solar panels, each 3.5 x 1.9 m in size, extend out from opposite sides of the craft. A 1.5 meter diameter parabolic high gain dish antenna is mounted on an adjacent side, and attached to a 2 meter boom, which is extended for mapping operations so the antenna is held away from the body of the spacecraft.
The spacecraft is three-axis stabilized with no scan platform. The main 596 N thruster wil use hydrazine and N2O4 propellant. Control is through 12 4.45 N hydrazine thrusters, mounted in four groups of three (two aft facing and one roll control thruster). The initial propellant load was 216.5 kg of hydrazine and 144 kg of N2O4. Four solar array panels (2 GaAs, 2 SI) provide 980 W of power to the spacecraft. Energy is stored in two 20 Amp-hr nickel hydrogen batteries, and supplied at 28 V DC. Temperature control is primarily passive with multilayer insulation, thermal radiators, and louvers, augmented by electrical heaters. Communications is achieved via the deep space network using the high gain antenna and two low gain antennas, one mounted on the high gain antenna and one on the equipment module. Uplink is in the X-band, downlink in the X and Ka bands. Minimum downlink rate is 21.33 kbps, 2 kbps engineering data downlink, and 10 bps emergency downlink.
The instruments on the nadir equipment deck consist of a camera, thermal emission spectrometer, laser altimeter, and a radio transmission relay. A magnetometer/electron reflectometer sensor is attached to the end of each solar array, and an ultra-stable oscillator is used for tracking and gravity determination. An 8086 processor is used for the payload data subsystem, and 1750A processors for the standard controls processor and the engineering data formatter. Data is stored on four 0.75 Gb solid state recorders.
After launch on a Delta 7925 (a Delta II Lite launch vehicle with nine strap-on solid-rocket boosters and a Star 48 (PAM-D) third stage) and a 10 month cruise phase, the Mars Global Surveyor was inserted into an elliptical capture orbit at 01:17 UT 12 September 1997. Over the next four months, it was intended that aerobraking maneuvers and thrusters would be used to lower the orbit to the final circular mapping orbit. However, one of the solar panels failed to latch properly when it was deployed and subsequently showed unexpected motion and moved past its fully deployed position when aerobraking began (thought to be due to the fracture of a damper arm and subsequent structural damage). A new aerobraking schedule was employed, which involved slower aerobraking putting less pressure on the solar panels through April 1998, at which time an 11.6 hour science phasing orbit with a 171 km periapsis was achieved and aerobraking was halted. After a 5 month hiatus, aerobraking was resumed on 23 September 1998. Science observations were made periodically during these maneuvers.
After aerobraking ended in February 1999, MGS was in a 118 minute circular polar science mapping orbit with an index altitude of 378 km. The orbit is sun-synchronous (2 a.m./2 p.m.) and maps over the 2 p.m. crossing from south to north (instead of north to south as originally planned). The orbit has a 7 day near-repeat cycle so Mars will be mapped in 26 day cycles. Science mapping began in mid-March 1999, which was summer in the northern hemisphere on Mars. The primary mission lasted one martian year (687 Earth days) through January, 2001. An extended mission took place until April 2002, further extensions were added until contact with the spacecraft was lost on 2 November 2006.
The Mars Global Surveyor mission cost about $154 million to develop and build and $65 million to launch. Mission operations and data analysis cost approximately $20 million/year.
NASA NSSDC Master Catalog Description
The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) experiment is designed to obtain images of the surface and atmosphere of Mars for studying the meteorology/climatology and geology of Mars. Its primary objectives are to: (1) obtain global, synoptic views of the Martian surface and atmosphere on a daily basis in order to understand the meteorological and climatological changes during the mission; (2) monitor surface and atmospheric features for changes on temporal scales from hours to years and on a spatial scale necessary for resolving the details of their morphology; and, (3) systematically examine local areas at high spatial resolution so that surface/atmosphere interactions and geologic processes which operate on short time scales can be quantified.
The MOC is the flight spare for the Mars Observer Camera, and hence is essentially identical. In order to acquire images to satisfy these three objectives, the MOC consists of a narrow-angle assembly and a wide-angle assembly. These two assemblies are contained within a single cylindrical structure, approximately 80 cm in length and 40 cm in diameter. The narrow-angle assembly, which comprises the principal part of the instrument, is a 35 cm aperture, 3.5 m focal length (f/10) Ritchey-Chretien telescope with a 0.4 degree field of view, filtered to operate in a band pass from 500-900 nm. The focal plane contains two 2048 element, 13 micrometer pixel CCD line arrays. This system is capable of providing an image resolution of 1.41 m/pixel at a nominal altitude of 380 km with an expected resolution of better than 1.5 m/pixel during the course of the mission. The wide-angle assembly consists of two cameras mounted on the side of the narrow-angle assembly. One wide-angle camera, optimized to operate in a band pass from 400-450 nm (``blue'') has a focal length of 11.4 mm (f/6.3). The other, designed to operate in a band pass from 575-625 nm (``red''), has a focal length of 11.0 mm (f/6.4). The wide angle instruments have fields of view of 140 degrees, with resolution of 280 m/pixel at nadir and 2 km/pixel at the limb. The focal plane contains two 3456 element, 7 micrometer pixel CCD line arrays. All three cameras are mounted in a fixed position on the nadir panel so that, during the mapping portion of the mission, they are always pointed toward Mars.
The electronics for the MOC are completely redundant and the narrow-angle and wide-angle cameras can be operated by either set of electronics and all three cameras can be operated simultaneously. The camera is controlled by a 32 bit (10 MHz, 1 MIPS) SA3300 microprocessor with four ASICs, 128 kbytes EPROM, and 192 kbytes SRAM. Because of the high volume of data which imaging experiments can generate, the MOC electronics contain not only a large amount of memory (~12 MB DRAM buffer) for processing and storing the images, but also have the capability of utilizing a number of data compression techniques (both lossless and lossy). Further, the MOC can transfer these data (either to the on-board recording system or via real-time transmission) at any rate of which the spacecraft is capable. As a result, the equivalent of two, four, or eight (depending on mission phase) 2048 x 2048 pixel images can be processed on record-only days and, once every three days on average, fourteen such images can be processed and sent during an eight-hour real-time pass. In-flight calibration of the MOC is extremely limited due to the fixed pointing of the instrument. Some opportunities for in-flight calibration are possible during regional or global dust storms. Otherwise, pre-flight measurements made to characterize the instrument performance comprised the bulk of the instrument calibrations. Available data rates are 700, 2856, 9120, and 29260 real-time bits/sec.
Finally, due to the MOC's large capacity for the storage and processing of images, it is intended to be used as part of the Mars Relay, which will provide a communications link between other Mars missions and the Earth.
|Mars Global Surveyor|
Credit: Manufacturer Image
Mars Global Surveyor entered a 258 x 54021 km x 93.3 deg polar orbit around Mars on 12 September 1997 after a 22 minute burn of its main engine. After a long aerobraking phase to a lower circular orbit, the spacecraft began its primary mission of photographing and observing changes on the Martian surface in March 1999. After nearly ten years of service, the last signals from MGS were received on 3 November 2006. The spacecraft went silent after an incorrect software upload caused its solar arrays to lose power.